It all depends on what you want in your bathroom/Kitchen. For example i fit bathrooms and kitchens and you may go to one job and the guy has got a full bathroom suite including taps for £399 from B&Q
You go to next job and the guy has got a bio jet bath, waterfall taps, water blade shower head, thermostatic diverter valves that need embeding in the walls, remote control showers and so on.
My own bathroom cost me around 5.0k materials only, but i have to say we have gone tottaly OTT with all the latest modern taps, designer rad, suspended laminate ceilling and waterfall bath fillers. it all depends on what needs doing once you rip out the old suite and unless you are planning to do a fair chunk of the work yourself the final costs would depend on labour you hire in.
I have done simular to DIY IS FUN, in addition built an extension on the side of the house. I did all the work myself at weekends and i do mean ALL.
I did it in any spare time i had. It took 12 months but we have totally gutted the house and done a complete re fit including new central heating, kitchen, bathroom, completely re plastered every downstairs wall (no bwoody drylining in my house) Removed dividing walls, bricked up doorways, extension, Conservatory the list is endless.
I know i wont re-coup the money i have thrown in unless the price of houses goes up massivly. But we are here for life now and have no plans in moving, so it doesnt matter to me. I'm happy